The present invention relates to a vacuum cleaner bag as well as a method of producing a vacuum cleaner bag.
Conventionally, vacuum cleaner bags have been constructed of paper. Paper bags are low cost and generally acceptable for removing and holding the large particles picked up by a vacuum cleaner. However, vacuum cleaners have become more effective at picking up fine particles and paper bags are typically quite inefficient at removing these fine-type particles from the vacuum cleaner air stream. These fine particles tend to remain in the air stream and are passed through the paper bag sidewalls with the exiting air creating significant amounts of indoor fine respirable particulate pollution. In order to reduce the amount of fine particulate discharged from the vacuum cleaner bag sidewalls, it has been proposed to employ a nonwoven fibrous filter layer in forming the vacuum cleaner bag. U.S. Pat. No. 4,589,894 proposes a filter layer that comprises a web of random synthetic polymeric microfibers, less than 10 microns in diameter on average. This filter layer web has a specific range of basis weights and air permeability. Further, in order to protect this relatively fragile filter layer, the filter layer is sandwiched between two more resilient outer nonwoven layers, for example, spun bond nonwoven webs.
U.S. Pat. No. 4,917,942 also addresses the problem of providing a vacuum cleaner bag with improved filtration efficiency against fine particles. The filter material comprises a microfiber web of synthetic polymers which web has been directly adhered to a support web. The microfiber web is charged to induce electrets, which provides a filter media having high capture efficiency for fine submicron particles with a low pressure drop.
Following the above two approaches are U.S. Pat. Nos. 5,080,702 and 5,306,534 in the name of Bosses. The '702 patent describes a disposable vacuum cleaner bag filter material which, like the '894 patent, comprises a microfiber web and a support layer. Like the '894 patent, the microfiber filter layer is not charged, however, unlike the '894 patent there is no inner support web. Like the '942 patent, no inner support layer is described as needed, however, unlike the '942 patent the filter web is not described as being charged. The patent examples exemplify that the melt blown microfiber web liner does not clog as rapidly as a standard cellulose (paper-like) liner. The examples also tested for resistance to tearing of the seams and of the paper when the filter was folded or flexed.
The U.S. Pat. No. 5,306,534 describes a charged filter web, which is attached to a textile fabric to form a reusable vacuum cleaner bag with high filter efficiency. The electret filter web material is a charged melt blown microfiber web (like the '942 patent) placed between two outer support layers (like the '894 patent), for example, described as spun bond materials. The charged melt blown microfiber filter web layer(s) and spunbond layers are pattern bonded together.
PCT Publication WO 93/21812 (Van Rossen) describes a vacuum cleaner bag, such as described in U.S. Pat. No. 4,917,942, which is provided with a scrim layer on the face opposite the vacuum cleaner hose inlet to provide specific abrasion resistance against large sand particles and the like. The scrim layer is bonded to the filter layer only at the vacuum cleaner bag end seams simplifying manufacturing.
Also commercially available is an industrial dust bag having an inner layer of a melt blown web (about 20 gm/m.sup.2) that is bonded only to the periphery of the bag. This bag is used as a copy machines toner particle bag and has an outer composite filter layer as described in U.S. Pat. No. 4,917,942, above.
The above patents all primarily address overall filter efficiency, particularly with respect to fine particles of a vacuum cleaner bag under normal-type operating conditions where a steady low concentration stream of particulates are being discharged into the bag. The present invention is directed at providing a filter bag with good fine particle removal efficiency over an extended period of time without filter blinding, which also has superior fine particle removal efficiency under shock loading conditions. Shock loading conditions occur when high concentrations of particles are discharged into the vacuum cleaner bag over a short period of time, such as where a vacuum cleaner is used to pick up a large pile of dust or debris. The invention is also concerned with providing a vacuum cleaner bag which displays a long service life without significant reduction in air flow or increase in pressure drop.